The present invention, relates to Pat. application, Ser. No. 12,548 filed Feb. 15, 1979, "Tail Rotor Control Cable Pylon Fold Accomodation", now U.S. Pat. No. 4,245,801, relates to cable guards for holding a cable in contact with a pulley.
The system described in the referenced application is concerned primarily with a particular type of helicopter in which a tail rotor pylon is foldable about a vertical hinge from a `closed` or flight position to an `open` or folded position in which it lies alongside the tail cone. In the closed position, the pylon forms an axial extension of the tail cone. The folding capability permits storage of the helicopter in a shipboard hangar or its handling in a ship elevator.
The invention, as described in that application, involves a system of pulleys and links capable of maintaining a constant tension in a rotor blade control cable during the folding and unfolding. Such a cable, as is known, usually extends from the pilot's compartment aft across the hinged connection of the pylon to the tail cone where it connects with the rotor blades to control their pitch during flight. Preferably, the connection is maintained during the folding operations. Consequently, the pulley and link system must be arranged to accomodate the hinged swing while maintaining cable tension. In general, the system includes a fixed tail cone pulley, a fixed tail rotor pulley and a floating pulley linked to the tail rotor pulley and carried at the free end of a radius arm which, itself, is pivotally mounted on the tail cone. The cable passes over these pulleys and swings with the floating pulley during folding.
The cable guard of the present invention primarily is intended for use with the pulley and link system of such a foldable helicopter. It is, however, adaptable for use with other pulley systems provided, of course, the other systems present comparable problems. In particular, difficulties have been experienced in providing the desired cable guarding or retaining capability for the cable wound on the fixed tail cone pulley of the system. Since the cable wound on this pulley swings away from the pulley during the folding operation, guard members cannot be mounted in a fixed position since they then would be in the path of the swinging cable and block the swing. To avoid this problem, it is possible to mount the guard on the radius arm so as to permit it to swing with the arm into and out of its cable guarding disposition. However, this solution presents its own difficulties. Thus, as experience has shown, when the arc of the swing is sufficiently wide, the guard still lies in the path of the swinging cable so that, to complete the swing, the cable must bend around the guard rather than swing in a straight line path. This bending or kinking rather quickly weakens the cable and promotes breakage due to premature fatigue.
It is therefore an object of the present invention to provide a cable guard capable of providing the desired cable retention without interfering with the cable during its swinging movement. As will be described, this object generally is achieved by mounting a particular guard member pivotally on the radius arm. The pivotal mounting permits the guard to yield to the cable contact.
A related object is to provide an arrangement which, regardless of its pivotal character, can be firmly set and locked in a precise position for achieving its primary cable guard function.